Methods and systems for efficiently acquiring towed streamer seismic surveys

ABSTRACT

Methods and systems for efficiently acquiring towed streamer marine seismic data are described. One method and system comprises positioning a plurality of source-only tow vessels and one or more source-streamer tow vessels to acquire a wide- and/or full-azimuth seismic survey without need for the spread to repeat a path once traversed. Another method and system allows surveying a sub-sea geologic feature using a marine seismic spread, the spread smartly negotiating at least one turn during the surveying, and shooting and recording during the turn. This abstract is provided to comply with the rules requiring an abstract, allowing a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to the field of marine seismic dataacquisition systems and methods of using same. More specifically, theinvention relates to systems and methods for acquiring towed streamerseismic surveys in less time, or using fewer seismic resources, orincreasing the fold using the same seismic resources.

2. Related Art

The performance of a marine seismic acquisition survey typicallyinvolves one or more vessels towing at least one seismic streamerthrough a body of water believed to overlie one or morehydrocarbon-bearing formations. WesternGeco L.L.C., Houston, Tex.,currently conducts high-resolution Q-Marine™ surveys, in some instancescovering many square kilometers. In many areas of the world hydrocarbonreservoirs located in structurally complex areas may not be adequatelyilluminated even with advanced towed marine streamer acquisitionmethods. For example, the shallow, structurally complex St. Josephreservoir off Malaysia produces oil and gas in an area that poses manysurveying and imaging challenges. Strong currents, numerous obstructionsand infrastructure, combined with difficult near-surface conditions, mayhinder conventional survey attempts to image faults, reservoir sands,salt domes, and other geologic features. A survey vessel known as aQ-Technology™ vessel may conduct seismic surveys towing multiple,1000-10,0000-meter cables with a separation of 25-50 meters, using theWesternGeco proprietary calibrated Q-Marine™ source. “Q” is theWesternGeco proprietary suite of advanced seismic technologies forenhanced reservoir location, description, and management. For additionalinformation on Q-Marine™, a fully calibrated, point-receiver marineseismic acquisition and processing system, as well as Q-Land™ andQ-Seabed™, see http://www.westerngeco.com/q-technology.

To achieve high density surveys in regions having a combination ofimaging and logistical challenges, a high trace density and closelyspaced streamers may be used, however, this presents the potential ofentangling and damaging streamer cables and associated equipment, unlessstreamer steering devices are closely monitored and controlled. Whilethe Q suite of advanced technologies for marine seismic data acquisitionand processing may provide detailed images desired for many reservoirmanagement decisions, including the ability to acquire wide- and/or fullazimuth data, the ability to acquire marine seismic data in less timeand with less cost, or to increase the fold while also increasing thediversity of azimuth and offset, are constant goals of the marineseismic industry and would be viewed as advances in the art.

SUMMARY OF THE INVENTION

In accordance with the present invention, systems and methods aredescribed for acquiring marine seismic data that may be more costeffective and provide improved seismic imaging in less time compared topresently employed systems and methods. While the systems and methods ofthe invention are particularly well-suited for collecting marine seismicdata using one or more towed streamer cables, the systems and methods ofthe invention may also be useful when employing seabed seismic receivercables.

A first aspect of the invention are methods of acquiring marine seismicdata, one method comprising:

-   (a) deploying a marine seismic spread comprising one or more sources    and a streamer tow vessel towing one or more marine seismic    streamers comprising a plurality of acoustic receivers, and    optionally a source;-   (b) surveying a sub-sea geologic feature using the marine seismic    spread, the spread smartly negotiating at least one turn during the    surveying; and-   (c) shooting at least one source and recording reflections using at    least some of the receivers from the sub-sea geologic feature during    the at least one turn.

A second method of the invention comprises:

-   (a) deploying a marine seismic spread comprising a plurality of    source-only tow vessels each towing one or more marine seismic    sources without streamers, and one or more source-streamer tow    vessels each towing one or more marine seismic sources and one or    more seismic streamers; and-   (b) positioning the source-only tow vessels and the source-streamer    tow vessels to acquire a wide- and/or full azimuth seismic survey    without need for the spread to repeat a path once traversed.

Methods of the invention include those wherein there is more than onestreamer in the spread, and the distance between streamers issubstantially maintained by a plurality of streamer steering devices,such as those known under the trade designation Q-FIN, available fromWesternGeco LLC, although the invention is not limited to thisparticular type of streamer steering device. Combinations of the methodsof the methods may be practiced within the invention, wherein shootingand recording during at least one turn is performed along withpositioning the source-only tow vessels and one or more source-streamertow vessels to acquire a wide- and/or full azimuth seismic surveywithout the need for the spread to repeat a path once traversed. Methodsof the invention include those wherein split-spread seismic data isacquired by acquiring seismic data simultaneously on one or more seismicsource lines, including embodiments wherein the deploying of one or moresource-streamer tow vessels comprises deploying a single source-streamertow vessel, and methods including deploying one or more source-only towvessels starboard of the streamers and one or more source-only towvessels positioned port of the streamers, wherein the starboard and portdistances are either the same or different. Certain other methods of theinvention include deploying one or more starboard source-only towvessels ahead of and starboard of the streamers, and one or moresource-only tow vessel behind and starboard of the streamers, whiledeploying a similar arrangement on the port side. Certain methods ofthis embodiment of the invention may comprise deploying two or morestreamer-source tow vessels each towing a plurality of streamers.

Other methods of the invention comprise collecting split-spread marineseismic data, comprising deploying a single source-streamer tow vesseltowing a plurality of streamers, and deploying all of the source-onlytow vessels on the starboard (or port) side of one or moresource-streamer tow members to acquire wide- and/or full azimuth seismicsurvey data. Certain of these method embodiments may comprise deployingtwo or more source-only tow vessels port of (or starboard of) andpositioned ahead of the streamers, and deploying two more source-onlytow vessels port of (or starboard of) and positioned behind thestreamers. A variation of these embodiments is deploying two or moresources utilizing the same source-only tow vessels.

Other methods of the invention comprise controlling the one or moresource-only tow vessels and/or the one or more source-streamer towvessels with one or more PI or PID controllers alone or in conjunctionwith other controllers. Certain methods of the invention may comprisetowing one or more source-streamer tow vessels wherein the streamers aretowed in configuration selected from side-by-side configuration,over/under configuration, “V” configuration, “W” configuration, or someother configuration.

Another aspect of the invention comprises systems, one systemcomprising:

-   (a) a marine seismic spread comprising one or more sources and a    streamer tow vessel adapted to tow one or more marine seismic    streamers comprising a plurality of acoustic receivers, and    optionally a source;-   (b) the spread adapted to survey a sub-sea geologic deposit using a    linear swath and equipped to smartly negotiate at least one turn    before or after the linear swath using the towed streamer marine    seismic spread.

Another system of the invention comprises:

-   (a) a marine seismic spread comprising a plurality of source-only    tow vessels each adapted to tow one or more marine seismic sources    without streamers, and one or more source-streamer tow vessels each    adapted to tow one or more marine seismic sources and one or more    seismic streamers;-   (b)the source-only tow vessels and the streamer-source tow vessel    adapted to be positioned to acquire a wide- and/or full azimuth    seismic survey without need for the spread to repeat a path once    traversed.

Systems of the invention include those which maybe termed “split-spread”systems. These embodiments would comprise passive and/or active sourcedeflecting members, such as source deflectors known in the art asMONOWING, available from WesternGeco L.L.C., and other sourcedeflectors, such as door-type deflectors.

The simultaneous acquisition of split spread seismic data may be adaptedto other marine seismic spread configurations known in the art, and allsystems of the invention may be adapted to acquire marine seismic dataduring “linear” as well as during “curvilinear” surveys or portions ofsurveys (for example during turns). Systems of the invention foracquiring marine seismic data during curvilinear surveys or portions ofsurveys may comprise one or more receiver positioning apparatus orsystems, source positioning apparatus or systems, one or more streamersteering devices, one or more source array steering devices, and/ornoise attenuation apparatus or systems. Systems known as Q-Marine™include these features and may be used in the systems and methods of theinvention advantageously. Further, all systems of the invention mayutilize sequential source shooting or, alternatively, two or moresources may be shot simultaneously, with the sources being encoded sothat they may be distinguished during data interpretation. For the samenominal shot point interval, firing two or more sources simultaneouslymay reduce the shot time interval on each source line compared withsequential shooting.

Another system embodiment of the invention is that wherein the pluralityof source-only tow vessels comprises two source-only tow vesselsfollowing substantially the same path or line, either port or starboardof a streamer-only tow vessel traveling substantially parallel to thepath of the source-only tow vessels. This split-spread arrangementallows collection of a single source line.

Systems and methods of the invention may benefit from one or morecontrollers that control position of one or more tracking points.Tracking points may be anywhere in the marine seismic spread, forexample but not limited to the center of a source, a streamer front endcenter, a streamer back end center, a tracking point somewhere between acenter of source and a streamer front end center, a center of aplurality of streamers, a front of any one streamer, and the like.Tracking points may be dynamically or non-dynamically moved within aspread to optimize a given steering strategy, particularly during dataacquisition during turns and other curvilinear paths. Controllers may bephysically a part of the vessel steering sub-system or locatedseparately from the steering sub-system, and may use some or allavailable information, including, but not limited to, source and vesselpositions, vessel gyroscope reading, vessel compass reading, vesselspeed log, streamer front end positions (if streamers are present), andhistorical, real-time, and future current and wind information andpredictions when calculating the residual difference, and thus these maytaken into consideration in the calculation of optimum vessel steeringpath by the vessel steering sub-system. The phrase “vessel steeringsub-system” is defined herein and may differ among the variousembodiments of the invention, as explained in the definition.Controllers may be selected from PI controllers, PID controllers(including any known or reasonably foreseeable variations of these), andcompute a residual equal to a difference between a tracking point 3Dcoordinate position and a pre-plot track, optionally together withcurrent and wind measurements, to produce a set point input to a vesselsteering algorithm used by a vessel steering sub-system. Controllers maycompute the residual continuously or non-continuously. Other possibleimplementations of the invention are those wherein one or morecontrollers comprise more specialized control strategies, such asstrategies selected from feed forward, cascade control, internalfeedback loops, model predictive control, neural networks, and Kalmanfiltering techniques. Systems and methods of the invention may be usedduring seismic data collection, including 3-D and 4-D seismic surveying.

Systems of the invention may include a seismic spread comprising one ormore vessels such as towing vessels, chase vessels, work vessels, one ormore a seismic sources, and optionally one or more seismic streamerstowed by towing vessels. The streamers and sources may be separatelytowed or towed by the same vessel. If towed by separate vessels, twocontrollers may be employed and two residuals computed. In general, thecontroller may compute the residual based on what the positionmeasurement system reports as the 3D coordinate position of the trackingpoint. Although there may be some degree of error in the reported 3Dcoordinate position due to a variety of error sources, includinginstrument measurement error, even with the errors the tracking pointmay be better controlled by steering the vessel the majority of thetime.

Systems and methods of the invention may optionally be used inconjunction with other systems and methods. For example, if the centersof each of the sources are tracking points, their 3D coordinatepositions may be determined from acoustic ranging networks, GPS, andother position sensors, and since the seismic team knows the paths eachtracking point is supposed to follow based on the survey specifications,the controllers may use at least that information to calculateresiduals, and a series of set points based on the residuals, for thesteering algorithms of each vessel, either to steer the vessels back tothe survey-specified paths, or ensure that the survey-specified pathsare adhered to.

Systems and methods of the invention will become more apparent uponreview of the brief description of the drawings, the detaileddescription, and the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The manner in which the objectives of the invention and other desirablecharacteristics can be obtained is explained in the followingdescription and attached drawings in which:

FIGS. 1-5 are plan or overhead schematic computerized renditions of fiveembodiments of systems and methods of the invention;

FIG. 6 is a computerized rendition of a plan view of one embodiment ofthe invention during a turning maneuver;

FIGS. 7-8 compare raw data acquired during the turn (FIG. 7) with thedata after noise attenuation (FIG. 8);

FIGS. 9-13 are schematic block diagrams illustrating a variety ofcontrol strategies useful in the present invention; and

FIG. 14 is a schematic plan view of one method of the invention foracquiring towed streamer marine seismic survey data, discussing howshooting and recording acoustic seismic data during spread turns mayincrease efficiency of towed streamer marine seismic data acquisitionmethods.

It is to be noted, however, that the appended drawings are not to scaleand illustrate only typical embodiments of this invention, and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details and that numerous variations ormodifications from the described embodiments may be possible. Forexample, in the discussion herein, aspects of the invention aredeveloped within the general context of acquiring marine seismic data inmore time and cost efficient manner, which may employcomputer-executable instructions, such as program modules, beingexecuted by one or more conventional computers. Generally, programmodules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Moreover, those skilled in the art will appreciatethat the invention may be practiced in whole or in part with othercomputer system configurations, including hand-held devices, personaldigital assistants, multiprocessor systems, microprocessor-based orprogrammable electronics, network PCs, minicomputers, mainframecomputers, and the like. In a distributed computer environment, programmodules may be located in both local and remote memory storage devices.It is noted, however, that modification to the systems and methodsdescribed herein may well be made without deviating from the scope ofthe present invention. Moreover, those skilled in the art willappreciate, from the discussion to follow, that the principles of theinvention may well be applied to other aspects of seismic dataacquisition. Thus, the systems and method described below are butillustrative implementations of a broader inventive concept.

All phrases, derivations, collocations and multiword expressions usedherein, in particular in the claims that follow, are expressly notlimited to nouns and verbs. It is apparent that meanings are not justexpressed by nouns and verbs or single words. Languages use a variety ofways to express content. The existence of inventive concepts and theways in which these are expressed varies in language-cultures. Forexample, many lexicalized compounds in Germanic languages are oftenexpressed as adjective-noun combinations, noun-preposition-nouncombinations or derivations in Romanic languages. The possibility toinclude phrases, derivations and collocations in the claims is essentialfor high-quality patents, making it possible to reduce expressions totheir conceptual content, and all possible conceptual combinations ofwords that are compatible with such content (either within a language oracross languages) are intended to be included in the used phrases.

The present invention relates to various systems and methods forefficiently acquiring marine seismic data, wherein efficiency may bedefined as more cost effective and provide improved seismic imaging inless time compared to presently employed systems and methods. Thesystems and methods may be particularly adept at acquiring wide- and/orfull azimuth marine seismic data, and acquiring such data duringcurvilinear paths, for example during spread turns.

As used herein the terms “smartly negotiate” and “smartly negotiating”mean that the streamers are steered through turns using controlledsteering of streamer steering devices, and position of each seismicacoustic receiver is determined during the turns through acousticnetworks, which may or may not be full streamer length acousticnetworks. This ability to control the motion of the streamers anddetermine positions of the receivers during turns allows the marineseismic team to gather valuable reservoir and geologic data withincreased efficiency. As used herein the term “turn” includes reversals,which is an art-recognized term used when a towed streamer marineseismic spread completes a first path or swath and makes a wide port orstarboard curved path that is continued until the second path or swathhas a heading 180° different than the first path or swath.

As used herein the phrase “wide- and/or full azimuth seismic survey”means acquiring marine seismic data through a range of (or all) anglesthat a direct line from a source to a receiver makes with true north.

The phrase “without the need for the spread to repeat a path oncetraversed” means that methods and systems of the invention do notrequire a marine seismic spread to repeat a particular path to obtainwide- and/or full azimuth seismic survey data. This may greatly savetime, effort, and cost of obtaining wide and/or full azimuth marineseismic data records.

The term “spread” and the phrase “seismic spread” are usedinterchangeably herein and mean the total number of components,including vessels, vehicles, and towed objects including cables, sourcesand receivers, that are used together to conduct a marine seismic dataacquisition survey.

The term “position”, when used as a noun, is broader than “depth” orlateral (horizontal) movement alone, and is intended to be synonymouswith “spatial relation.” Thus “vertical position” includes depth, butalso distance from the seabed or distance above or below a submerged orsemi-submerged object, or an object having portions submerged. When usedas a verb, “position” means cause to be in a desired place, state, orspatial relation. The term may also include orientation, such asrotational orientation, pitch, yaw, and the like.

FIGS. 1-5 are plan or overhead schematic computerized views of fiveembodiments of systems and methods of the invention. The embodimentsrepresented schematically in FIGS. 1-4 allow split-spread seismic datato be acquired simultaneously on two seismic sources lines. One benefitof acquiring two source lines simultaneously is a reduction in theacquisition time by half. Other configurations may produce commensuratetime savings. Referring to FIG. 1, source-only vessels S1 and S2 travelto the left in the schematic, as does source-streamer vessel S3, andsource-only vessels S4 and S5. Source-only vessels S1 and S2 tow sourcesto the front-port and front-starboard, respectively, while source-onlyvessels S4 and S5 tow sources to the back-port and back-starboard,respectively. Source-only vessels S1 and S4 travel approximately thesame port line, while source-only vessels S2 and S4 travel the samestarboard line. Meanwhile, source-streamer vessel S3 tows a source aswell as 10 streamer cables, designated as Sn. The number of streamercables may vary as desired depending on the data to be gathered.Anywhere from 1 to 20 streamers are typical. In FIG. 1 the streamers areequal in length and at the same depth, but these are not necessaryparameters for the invention. Streamers Sn are each shown to be about7000 meters in this embodiment. The sources towed by source-only vesselsS1 and S2 are separated in the y-coordinate, which is approximatelyperpendicular to the direction of travel of the spread, from the sourcetowed by source-streamer vessel S3 by distances as indicated by arrowd2. The cross-line distances S1-S2 and S1-S3 may be the same ordifferent. In this embodiment d2 is about 1500 meters port for S1, andabout 1500 meters starboard for S2. Arrow d1 indicates a distance in theX-coordinate, or in-line direction of travel, between S1 and S3, as wellas between S2 and S3, although these distances may be the same ordifferent. In this example, d1 is about 500 meters. Distance d3represents the distance in the X-coordinate between sources towed bysource-only tow vessels S2 and S5, as well as between the sources towedby source-only tow vessels S1 and S3, although the distances S1-S4 andS2-S5 may be the same or different. Distance d3 may vary as required byany particular survey; in this embodiment distance d3 is about 9000meters. Distance d4 (FIGS. 2 and 4) is at least one half of the width ofthe spread plus from about 50 to about 500 meters, and distance d5 (FIG.4) is similar to distance d2 of FIG. 2.

FIG. 3 illustrates schematically a variation of the embodiment depictedin FIG. 1, the difference being that source-streamer vessel S3 in FIG. 1has been split into two sources S3 and S3′, with each of source-streamervessels S3 and S3′ towing five streamers.

In operation of the embodiments of FIGS. 1 and 3, as vessels S1, S2, S3,(S3′ in FIG. 3), S4, and S5 travel forward (to the left in FIGS. 1 and3), the sources may be fired either sequentially or in some othermanner, and receivers in streamers Sn collect data. Since there are twosource signaling lines (line S1-S4 and line S2-S5), as well as signalsfrom S3, the sub-sea geologic formations between lines S1-S4 and S2-S5may be collected without the need for the spread to traverse the samepath twice.

FIGS. 2 and 4 illustrate slightly different embodiments for reducing thetime of acquisition of split-spread marine seismic data by half. Theembodiment of FIG. 2 illustrates four sources-only tow vessels and theirassociated sources S1, S2, S4, and S5, while a source-streamer towvessel and its associated source S3 also tows eight streamers Sn. Inthis representative embodiment, as well as the embodiment depicted inFIG. 4, all source-only tow vessels are on the port side of thestreamers. They could just as well all be on the starboard side.Distance d1 represent a distance between sources associated withsource-only tow vessel S1 and the source associated with source-streamertow vessel S3. Distance d1 also represents the distance between thesource associated with source-only tow vessel S2 and the sourceassociated with source-streamer tow vessel S3. Distance d1 may vary asdesired for any particular survey; in this embodiment distance d1 isabout 1000 meters. Distance d2 represents the distance between sourcesassociated with source-only tow vessels S1 and S2, as well as hedistance between sources associated with source-only tow vessels S4 andS5. Distance d2 between S1 and S2 may be substantially equal to thedistance d2 between S4 and S5, although exact identity is not required.Distance d2 may also vary as desired for any particular survey; in thisembodiment distance d2 is about 1000 meters. Distance d3 represents thedistance in the X-coordinate between sources towed by source-only towvessels S1 and S4, as well as between the sources towed by source-onlytow vessels S2 and S5, although the distances S1-S4 and S2-S5 may be thesame or different. Distance d3 may vary as required by any particularsurvey; in this embodiment distance d3 is about 12000 meters, but couldbe 30000 m or more. Distance d4 represents the distance in theY-coordinate between the source towed by source-only tow vessel S2 andthe source associated with source-streamer vessel S3. Distance d4 mayvary as required by any particular survey; in this embodiment distanced4 is about 2000 meters.

FIG. 4 illustrates a slightly different embodiment, wherein twosource-only tow vessels S1 and S2 of FIG. 2 are replaced with onesource-only tow vessel S6, configured to tow both sources S1′ and S2′.Sources S1′ and S2′ may be deflected to port and starboard,respectively, using known deflectors.

In operation of the embodiments of FIGS. 2 and 4, as vessels S1, S2, S3,S4, S5 (and S6 in FIG. 4) travel forward (to the left in FIGS. 2 and 4),the sources may be fired either sequentially or in some other manner,and receivers in streamers Sn collect data. Since there are two sourcesignaling lines (lines S1-S4 and S2-S5 in FIG. 2, and lines S1′-S4 andS2′-S5 in FIG. 4), as well as signals from S3, the sub-sea geologicformations between these lines may be collected without the need for thespread to traverse the same path twice.

FIG. 5 is a simplified schematic representation of another system andmethod of the invention, illustrating a split-spread marine seismic dataacquisition of a single source line between two sources associated withsource-only tow vessels S1 and S2 using one streamer-only tow vessel S.Distance d1 represents the distance between source S1 and a center lineof a group of streamers represented by Sn. Distance d2 represents thedistance between sources associated with source-only tow vessels S1 andS2. Two different times are represented, time t1 and time t2. Inoperation, as streamer-only vessel S, and source-only vessels S1 and S2travel forward with the same speed (to the right), at time t1, sourcesassociated with source-only vessels S1 and S2 may fire simultaneously,acquiring a seismic data line. At time t2, the sources may again firesimultaneously. Alternatively, the source associated with source-onlyvessel S1 may fire at time t1 while the source associated withsource-only vessel S2 remains idle at time t1, while the sourceassociated with source-only vessel S2 fires at time t2 and the sourceassociated with source-only vessel S1 remains idle. Each shot pointfired by the source S2 will be re-occupied by the source S1 and in thisway a split-spread will be generated: for shot S2 the spread is behindthe source point and for source S1, when S1 will be at the same locationwith S2, the spread will be in front of the source point. Either firingarrangement allows collection of data from a single line without thespread having to traverse the same path again, as might be required withstandard spreads.

FIG. 6 is a time-lapsed computerized plan view of one system and methodembodiment of the invention during a turning maneuver. In the embodimentillustrated, which comprises a source-streamer tow vessel pulling eightstreamers, the distance between vertical dotted lines is 1000 meters,while the distance between horizontal dashed lines is also 1000 meters.Thus the turn for this embodiment occurred over an area of about 17000meters (Y-coordinate) by 12000 meters (X-coordinate). Wide-azimuthand/or full-azimuth data may be collected during such a curvilinear pathusing, for example, one of the embodiments illustrated in FIGS. 1-4,along with spread control devices as described herein, and with thefully calibrated sources known as Q-Marine™, from WesternGeco L.L.C.,Houston, Texas. The ability to collect wide-angle and/or full-angleazimuth marine seismic data during turns or other curvilinear pathsgreatly reduces the time and cost of obtaining this marine seismic data.

FIGS. 7-8 compare raw data acquired during the turn (FIG. 7) with thedata after noise attenuation using the Q-marine single sensor processing(FIG. 8). Data acquired during the turns with standard marine systems isquite noisy due to the marine current flow along the non-steeredstreamers. Streamer steering reduces noise due to marine current. Therecording of single sensor data makes possible to attenuate the turningnoise efficiently (FIG. 8 vs. FIG. 7). Furthermore, conventional systemscannot estimate position of the receivers accurately enough during theturns; this is possible with the methods and systems of the invention.

FIGS. 9-13 are schematic block diagrams of five non-limiting systems andmethods for controlling positions of one or more track points TP usingvessel steering, which may be useful in efficiently collecting towedstreamer marine seismic data in accordance with the invention. Thesecontrol strategies may be used for gross steering of sources and/orstreamers towed by one or more vessels, while spread control elementssuch as steerable birds and source steering devices may be used forfiner steering.

In the discussion that follows, the phrase “center of source”, sometimesreferred to herein as CS, means the 3D coordinate position of the centerof a plurality of air-guns or other acoustic devices designed to produceacoustic signals, or “shots,” which are directed down through the waterinto the earth beneath, where they are reflected from the variousstrata.

The phrase “streamer front end center”, sometimes referred to herein asSFC, means the 3D coordinate position of a plurality of streamer frontends determined from the individual 3D coordinate positions of eachstreamer front end, that is, the streamer ends closest to the towingvessel.

The term “control”, used as a transitive verb, means to verify orregulate by comparing with a standard or desired value. Control may beclosed loop, feedback, feed-forward, cascade, model predictive,adaptive, heuristic and combinations thereof.

The term “controller” means a device at least capable of accepting inputfrom sensors and meters in real time or near-real time, and sendingcommands directly to a vessel steering sub-system, and optionally tospread control elements, and/or to local devices associated with spreadcontrol elements able to accept commands. A controller may also becapable of accepting input from human operators; accessing databases,such as relational databases; sending data to and accessing data indatabases, data warehouses or data marts; and sending information to andaccepting input from a display device readable by a human. A controllermay also interface with or have integrated therewith one or moresoftware application modules, and may supervise interaction betweendatabases and one or more software application modules.

The phrase “PID controller” means a controller using proportional,integral, and derivative features, as further explained herein. In somecases the derivative mode may not be used or its influence reducedsignificantly so that the controller may be deemed a PI controller. Itwill also be recognized by those of skill in the control art that thereare existing variations of PI and PID controllers, depending on how thediscretization is performed. These known and foreseeable variations ofPI, PID and other controllers are considered useful in practicing themethods and systems of the invention.

The phrase “spread control element” means a spread component that iscontrollable and is capable of causing a spread component to changecoordinates, either vertically, horizontally, or both, and may or maynot be remotely controlled.

The terms “control position”, “position controllable”, “remotelycontrolling position” and “steering” are generally used interchangeablyherein, although it will be recognized by those of skill in the art that“steering” usually refers to following a defined path, while “controlposition”, “position controllable”, and “remotely controlling position”could mean steering, but also could mean merely maintaining position. Inthe context of the following discussion, “control position” means we useat least the tracking point position and compare it to a pre-plot pathin order to give steering commands to vessel steering elements.

“Real-time” means dataflow that occurs without any delay added beyondthe minimum required for generation of the dataflow components. Itimplies that there is no major gap between the storage of information inthe dataflow and the retrieval of that information. There may be afurther requirement that the dataflow components are generatedsufficiently rapidly to allow control decisions using them to be madesufficiently early to be effective. “Sear-real-time” means dataflow thathas been delayed in some way, such as to allow the calculation ofresults using symmetrical filters. Typically, decisions made with thistype of dataflow are for the enhancement of real-time decisions. Bothreal-time and near-real-time dataflows are used immediately after thenext process in the decision line receives them.

The phrase “vessel steering sub-system” means any device or collectionof components that are capable of generating commands to vessel steeringelements, such as rudders, thrusters, and the like, to accomplish theintended movements of the seismic towing vessel. In some embodiments thevessel steering sub-system may include a vessel tracking computer and/oran autopilot. In other embodiments a vessel steering sub-system maybypass conventional tracking and autopilot functions, and may be simplya vessel rudder controller, and/or a vessel thruster controller (theseembodiments may be referred to as “steering the vessel directly” usingthe controller). In yet other embodiments, all of these components(tracking computer, autopilot, rudder controller, and thrustercontrollers) may be employed.

Referring now to FIGS. 9-13, note that the same numerals are usedthroughout FIGS. 9-13 to designate same components unless otherwisementioned. FIG. 9 illustrates a simple PID feedback loop. The maincomponents include the vessel 2, a tracking point 4, in a block labeledTP which may be an imaginary point anywhere in the spread, such asbetween the center of a source and a streamer front end center, or maybe the center of a source itself. Also illustrated are blocks 6 for anautopilot AP, a block 8 designating a tracking control device T, and PIDcontroller 10. PID controller 10 compares a set point pre-plot position1 of tracking point 4 with a measured 3D coordinate position 3 oftracking point 4, and calculates a difference, referred to herein as aresidual or residual difference, 5, and generates a command 7 as a setpoint track to tracking control device 8. It will be understood thatcertain embodiments will send command 7 directly to the autopilot,bypassing the tracking device, or bypass both the tracking device andautopilot, and directly command the vessel rudder and/or vesselthruster, as indicated by the dashed line 77. In one embodiment of FIG.9, tracking control device 8 compares this new set point track 7 to ameasured track 9 b of vessel 2 and computes a difference 11, and usesdifference 11 in generating a set point heading 13 for use by autopilot6. Autopilot 6 compares set point heading 13 with a measured heading 9 aof vessel 2, computes a difference as 15, and uses difference 15 togenerate a steering set point 17 for vessel 2, which is transmitted to avessel rudder and/or thruster. Steering of vessel 2 will then influencethe tracking point 4 position in a more controlled and stable fashionusing a tuned controller, rather than a human operator. In onealternative embodiment, indicated by dashed line 77, steering set point17 is replaced directly by set point indicated by dashed line 77.

FIG. 10 illustrates a schematic block diagram of another system andmethod useful in the invention for controlling position of a track pointTP using vessel steering. Components 2, 4, 6, 8, and 10 are the same asin FIG. 9. PID controller 10 compares a pre-plot position 1 of trackingpoint 4 with a measured 3D coordinate position 37 of tracking point 4,and calculates a difference, referred to herein as a residual orresidual difference, 5, and generates a command 7 as a set point trackto tracking control device 8. Added in this embodiment is a modificationof the set point signal 7 by a feed-forward controller 12 in block C,which may optionally feed historical, real time or near-real time, orfuture predictions of data 19 regarding current and/or wind as amodification to set point 7. Also depicted is a block denoted FF, whichmay optionally feed forward historical information 19 regarding wind,current, and other environmental conditions, or information regardingobstructions in the designated survey area, and the like. In oneembodiment of FIG. 3, a modified set point track 25 is compared with ameasured track 35 b of vessel 2 and computes a difference 27, and usesdifference 27 in generating a set point heading 29 for use by autopilot6. Autopilot 6 compares set point heading 29 with a measured heading 35a of vessel 2, computes a difference as 31, and uses difference 31 togenerate a steering set point 33 for vessel 2. Alternatively, ratherthan comparing set point 25 with measured track 35 b, set point 77 issent directly to vessel 2 for changing a vessel rudder, thruster, orboth. In either embodiment of FIG. 10, steering of vessel 2 will theninfluence the tracking point 4 position in a more controlled and stablefashion using a tuned PID controller and feed-forward controller, ratherthan a PID controller alone, or a human operator.

FIG. 11 illustrates another system and method useful in the invention inschematic block diagram fashion. The system and method illustrated inFIG. 11 is similar to that illustrated in FIG. 9, but includes certainfeatures not present in the embodiment illustrated in FIG. 9. Ratherthan a single tracking point and a single pre-plot tracking point, theembodiment of FIG. 11 includes three pre-plot track set points 1 a, 1 b,and 1 c. Pre-plot set point 1 a may be for a center of source, CS;pre-plot set point 1 b may be for a streamer front end center, SFC; andpre-plot set point 1 c may be for an imaginary tracking point, TP. Otherpre-plot set points may be used. Also included in this embodiment arethree PID controllers 10 a, 10 b, and 10 c, one each for calculatingrespective residual differences 5 a, 5 b, and 5 c between respective setpoints 1 a, 1 b, and 1 c and 3D coordinate position measurements 3 a, 3b, and 3 c for CS, SFC, and TP, and generating preliminary command setpoints 7 a, 7 b, and 7 c, respectively. A switch SW, which may beautomatically programmed, or periodically switched by a human operator,selects which preliminary command set point to use as the set point 7for tracking control device 8. As an example, switch SW might beprogrammed to compare preliminary set points 7 a, 7 b, and 7 cto selectthe largest of the residuals to use. Although the expense of this systemmay be greater than the embodiment illustrated in FIG. 9 due to theprovision of three PID (or other type) controllers and a switchingdevice, the ability to use the greatest residual, or some otherresidual, may provide higher quality control. Mono-variable ormultivariable model predictive controllers could substitute for one ormore of the PID controllers in these embodiments.

FIGS. 12 and 13 illustrate use of Model Predictive (MP) controllersrather than PID controllers. The characteristics of each are discussedherein below. The embodiments illustrated in FIG. 12 are similar tothose discussed in relation to FIG. 9 except for the use of MPcontrollers, which may be mono-variable or multivariable MP controllers.The main components include the vessel 2, a tracking point 4, in a blocklabeled TP which may be an imaginary point anywhere in the spread, suchas between the center of source and streamer front end center, or may bethe center of source itself. Also illustrated are blocks 6 for anautopilot AP, a block 8 designating a tracking control device T, and MPcontroller 10. MP controller 10 compares a set point pre-plot position 1of tracking point 4 with a measured 3D coordinate position 3 of trackingpoint 4, and uses a pre-existing mathematical model of the system inconjunction with measured disturbances 191 on the system, such as wind,currents, and the like, and calculates a residual and generates acommand 7 as a set point track to tracking control device 8. As with theembodiments described in reference to FIG. 9, it will be understood thatcertain embodiments will send command 7 directly to the autopilot,bypassing the tracking device, or bypass both the tracking device andautopilot, and directly command the vessel rudder and/or vesselthruster, as indicated by the dashed line 77. In one embodiment of FIG.12, tracking control device 8 compares this new set point track 7 to ameasured track 9 b of vessel 2 and computes a difference 11, and usesdifference 11 in generating a set point heading 13 for use by autopilot6. Autopilot 6 compares set point heading 13 with a measured heading 9 aof vessel 2, computes a difference as 15, and uses difference 15 togenerate a steering set point 17 for vessel 2, which is transmitted to avessel rudder and/or thruster. Steering of vessel 2 will then influencethe tracking point 4 position in a more controlled and stable fashionusing a tuned controller, rather than a human operator. In onealternative embodiment, indicated by dashed line 77, steering set point17 is replaced directly by set point indicated by dashed line 77.

The embodiments illustrated in FIG. 13 are similar to those discussed inrelation to FIG. 10 except for the use of MP controllers, which may bemono-variable or multivariable MP controllers. MP controller 10 comparesa pre-plot position 1 of tracking point 4 with a measured 3D coordinateposition 37 of tracking point 4, and calculates a residual 5, andgenerates a command 7 as a set point track to tracking control device 8.Added in this embodiment is a modification of the set point signal 7 bya feed-forward controller 12 in block C, which may optionally feedhistorical, real time or near-real time, or future predictions of data19 regarding current and/or wind as a modification to set point 7. Alsodepicted is a block denoted FF, which may optionally feed forwardhistorical information 19 regarding wind, current, and otherenvironmental conditions, or information regarding obstructions in thedesignated survey area, and the like. In one embodiment of FIG. 13, amodified set point track 25 is compared with a measured track 35 b ofvessel 2 and computes a difference 27, and uses difference 27 ingenerating a set point heading 29 for use by autopilot 6. Autopilot 6compares set point heading 29 with a measured heading 35 a of vessel 2,computes a difference as 31, and uses difference 31 to generate asteering set point 33 for vessel 2. Alternatively, rather than comparingset point 25 with measured track 35 b, set point 77 is sent directly tovessel 2 for changing a vessel rudder, thruster, or both. In eitherembodiment of FIG. 13, steering of vessel 2 will then influence thetracking point 4 position in a more controlled and stable fashion usingan MP controller and feed-forward controller, rather than an MPcontroller alone, or a human operator.

The apparatus and methods illustrated in FIGS. 9-13, or other systemsand methods, may be used in conjunction with conventional spread controldevices. These devices include source steering devices and streamersteering devices. Such devices are often part of the spread and towed bythe vessel.

For example, a source reference point generally must be within 10 meterscross line of the target in order for a source steering device with anability to move the source 10 meters crossline to move the sourcereference closer to the target.

Controllers useful in the systems and methods of the invention may varyin their details. One PID controller useful in the invention may beexpressed mathematically as in Equation 1:u(t)=K _(p) [e(t)+1/T _(i) ·∫e(t)dt+T _(d) ·è(t)]  (1)wherein:

-   ∫ means integrate;-   è(t) means the time derivative;-   u(t) is controller output, either meters across to a tracking    control device such as that known under the trade designation    Robtrack/STS500, or heading to an autopilot;-   e(t) means difference between wanted (planned, reference) and    measured (current position, y) value;-   T_(d) is a constant for describing the derivative part of the    algorithm (the derivative part may be filtered to avoid deriving    high frequencies);-   T_(i) is a constant for describing the integrating part of the    algorithm; and-   K_(p) is a proportional gain constant.

In the s-plane (Laplace), the PID controller may be expressed as(Equation 2):H _(r)(S)=K_(p)[1+1/T _(i) s+T _(d) s/(1+T _(f) s)]  (2)wherein:

-   s is the variable in the s-plane; and-   T_(f) is a constant describing the filtering part of the derivative    part of the algorithm.

For discretization, a variety of transforms may be employed, and someconstants may or may not be useful. For example, the T_(f) constant maynot be necessary in some instances, but may be especially useful inother scenarios. As one discretization example, the z-transform may beused, meaning that the integral part of the algorithm may beapproximated by using a trapezoid model of the form (Equation 3):s=(1−z⁻¹)/T  (3)while the derivative part may be approximated using an Euler model(Equation 4):s=2/T·(1−z ⁻¹)/(1+z⁻¹)  (4)wherein T is the sampling time.

The resulting discrete model may then be used directly in the steeringalgorithm. Other discrete models, derived using other transforms, areuseful in the invention, and will be apparent to control technicians orcontrol engineers of ordinary skill.

Model Predictive Control (MPC) is an advanced multivariable controlmethod for use in multiple input/multiple output (MIMO) systems. Anoverview of industrial Model Predictive Control can be found at:www.che.utexas.edu/˜qin/cpcv/cpcv14.html. MPC computes a sequence ofmanipulated variable adjustments in order to optimise the futurebehavior of the process in question. At each control time k, MPC solvesa dynamic optimization problem using a model of the controlled system,so as to optimize future behavior (at time k+1, k+2 . . . k+n) over aprediction horizon n. This is again performed at time k+1, k+2 . . . .MPC may use any derived objective function, such as QuadraticPerformance Objective, and the like, including weighting functions ofmanipulated variables and measurements. Dynamics of the process and/orsystem to be controlled are described in an explicit model of theprocess and/or system, which may be obtained for example by mathematicalmodeling, or estimated from test data of the real process and/or system.Some techniques to determine some of the dynamics of the system and/orprocess to be controlled include step response models, impulse responsemodels, and other linear or non-linear models. Often an accurate modelis not necessary. Input and output constraints may be included in theproblem formulation so that future constraint violations are anticipatedand prevented, such as hard constraints, soft constraints, set pointconstraints, funnel constraints, return on capital constraints, and thelike. It may be difficult to explicitly state stability of an MPCcontrol scheme, and in certain embodiments of the present invention itmay be necessary to use nonlinear MPC. In so-called advance spreadcontrol of marine seismic spreads, PIED control may be used on strongmono-variable loops with few or nonproblematic interactions, while oneor more networks of MPC might be used, or other multivariable controlstructures, for strong interconnected loops. Furthermore, computing timeconsiderations may be a limiting factor. Some embodiments may employnonlinear MPC.

Feed forward algorithms, if used, will in the most general sense be taskspecific, meaning that they will be specially designed to the task theyare designed to solve. This specific design might be difficult todesign, but a lot is gained by using a more general algorithm, such as afirst or second order filter with a given gain and time constants.

The introduction of a tracking point may serve at least two purposes:

-   1. It gives a more flexible solution for a track that we want parts    of the spread to follow;-   2. If other means are used for controlling source positions, like a    winch or a source deflector, the vessel will in many occasions have    “spare” steering capacity available. This may mean that by moving    the tracking point aft of the sources, streamer front ends and    consequentially also the receivers may be closer to where they    should be, which may help the streamer steering devices, such as    those known under the trade designation Q-FIN, available from    WesternGeco, L.L.C., Houston, Tex., in achieving their steering    objectives.

In certain embodiments, a tracking point will not be a static point inthe spread, as time varying currents may result in the center of sourcesteering objective and the tracking point steering objective unable tobe met at the same time. In these embodiments, the tracking point may bemoved, either dynamically or non-dynamically, until both objectives canbe met with a certain slack. The reverse might also be the case, i.e.having excess steering power resulting in moving the tracking pointfurther aft. If the movement of the tracking point is above a predefineddistance, a new set of parameters for both the controller and the feedforward controller may be used to optimize the controller performance.

The control systems and methods illustrated in FIGS. 9-13 may be used inthe spread embodiments of FIGS. 1-6, the methods discussed in referenceto FIG. 14, as well as other spread configurations. For example, forobtaining deghosted seismic data, it may be possible to provide one ormore seismic streamers with a companion seismic streamer where thecompanions are towed in over/under fashion. The vertical distancebetween seismic streamers in an over/under seismic streamer pair mayrange from 1 meter to 50 meters, and may be about 5 meters. A selectednumber of hydrophones, either mounted within the seismic streamer orin/on equipment mounted onto the seismic streamer, may be used asreceivers in an acoustic ranging system and thereby provide knowledge ofthe horizontal and vertical position of seismic streamers.

In use, control systems and methods such as those illustrated in FIGS.9-13 are particularly adept for 3D and so-called 4D marine seismic dataacquisition surveys, for collection of wide- and/or full azimuth data,for shooting and recording towed streamer marine seismic data duringturns, and may be used in positioning seabed seismic cables as well.More specifically, the systems and methods of FIGS. 9-13 may beintegrated into the seismic towing vessel steering strategy, and may beintegrated into positioning strategies for the other spread elements.

FIG. 14 is a schematic plan view of one method of the invention foracquiring towed streamer marine seismic survey data, discussing howshooting and recording acoustic seismic data during spread turns mayincrease efficiency of towed streamer marine seismic data acquisitionmethods. FIG. 14 illustrates a hydrocarbon deposit or other sub-seageologic feature 200 of interest. Illustrated in FIG. 14 in plan viewschematically is the path of a towed streamer marine seismic spread. Thespread may be a single source-streamer vessel towing any number ofstreamers and seismic sources. Single- and dual-sources are common.Alternatively any of the spreads discussed herein may be used. Thespread might comprise, for example, three vessels, one of which is asource-streamer vessel, and the other two being source-only vessels, thesource-streamer vessel towing a dual source, and towing 8 streamers each8 km long, separated by 140 m, the source-only vessels each towing asingle source. The spread moves from right to left (which may, forexample, be east to west, or 90° azimuth, although this is arbitrary)beginning at 202, sails west past the geologic feature 200, thenperforms a looping 180° turn in turn area 206 and begins traveling leftto right (east), sails over the geologic feature, until finallyperforming another 180° turn in turn area 208 and coming very close to,but not exactly to the beginning point 202, wherein another sailingcycle is performed, the next sailing cycle moving just to the south ofthe previous sailing cycle, until the spread reaches point 204, thefinish of the seismic survey. A survey area consists in an image area,210, plus the area required to properly image the data (migrationaperture), 212, plus the area required to generate full fold data (foldtaper), 214. The fold coverage in the area of fold taper 214 iscontinually decreasing toward the edges of the survey, particularly inthe turn areas 206 and 208. By shooting during turns 206 and 208, thefold coverage is maintained the same. One advantage of shootingcontinuously during the turns is that the image area 210 is increasedand the extent of the whole survey is increased by adding area coveredduring turns. In this way, within the same acquisition time frame, alarger survey area is acquired with no additional acquisition time. Theacquisition during the turns is very beneficial for wide azimuthacquisition, which may require combinations of rectilinear andcurvilinear boat paths, as depicted in FIG. 14. Other combinations ofrectilinear and curvilinear vessel paths are considered within theinvention.

In order to acquire towed streamer marine seismic data during turns, theposition of acoustic receivers, streamer steering, and noise attenuationare key factors. The source-streamer vessel and streamers may be part ofa system known under the trade designation Q-Marine™, from WesternGeco.In these systems, streamers may be equipped with acoustic transmittersand point receivers for accurate position determination, employingintrinsic ranging modulated acoustics, as taught in U.S. Pat. No.5,668,775, incorporated by reference herein in its entirety. As taughtin the 775 patent, the streamer transmitters and point receivers mayform a full-streamer-length acoustic network, wherein a unique spreadspectrum code of acoustic frequencies are emitted by each of a pluralityof acoustic transmitters placed within the streamers, all frequenciesbeing within the seismic frequencies detected by the same receiversduring shooting and recording, and the point receivers within thestreamers are able to distinguish each transmitter's unique code. Thus,accurate positioning of seismic receivers is possible. Conventionalstreamers use arrays of hydrophones, such as 12 or 18 hydrophones pergroup, which are summed together in analog fashion and than recorded.Systems known as Q-Marine™ use single sensors or point receivers: theseare placed in the streamer at intervals, for example one every 3 to 4 m,and recorded. All point receivers route data to a computer, wheredigital filters are applied taking advantage of the very fine samplingof the receivers for very powerful coherent noise attenuation of lineswell noise and/or streamer cable noise. During the turns the noise frommarine current may be stronger, since at least portions of the streamersmay be traveling cross-current. This is one reason shooting during turnsis not possible with conventional streamers. With systems known asQ-Marine™, noise can be attenuated from each point receiver very well.Furthermore, streamers may be steered into desired positions by steeringdevices, as further described herein.

Shooting and recording in the turns is made possible through thecombination of steering of streamers and acoustic positioning networks,and optionally noise attenuation if necessary through digital filteringsignals from point receivers in the streamers. Furthermore, the abilityto acquire towed streamer marine seismic data during curved paths,turns, and the like increases efficiency since more data is obtainedduring the same survey time. Alternatively, less time is required toobtain the same amount of towed streamer seismic data. Less operatingtime translates into fuel and other operating savings forsource-streamer vessels, as well as source-only vessels.

Systems and methods of the invention may employ any number of spreadcontrol elements, which may include one or more orientation members, adevice capable of movements that may result in any one or multiplestraight line or curved path movements of a spread element in3-dimensions, such as lateral, vertical up, vertical down, horizontal,and combinations thereof. The terms and phrases “bird”, “cablecontroller”, “streamer control device”, and like terms and phrases areused interchangeably herein and refer to orientation members having oneor more control surfaces attached thereto or a part thereof. A“steerable front-end deflector” (or simply “deflector”) such astypically positioned at the front end of selected streamers, and otherdeflecting members, such as those that may be employed at the front endof seismic sources or source arrays, may function as orientation membersin some embodiments, although they are primarily used to pull streamersand steer sources laterally with respect to direction of movement of atow vessel. Horizontal separation between individual streamers may rangefrom 10 to about 200 meters. In the embodiments of FIGS. 1-4 thehorizontal streamer separation may be consistent between one streamerand its nearest neighboring streamers. Horizontal and/or verticalcontrol of streamers may be provided by orientation members (notillustrated) which may be of any type as explained herein, such as smallhydrofoils or steerable birds that can provide forces in the verticaland/or horizontal planes. One suitable orientation member is the deviceknown under the trade designation Q-FIN™, available from WesternGecoL.L.C., Houston, Tex., and described in U.S. Pat. No. 6,671,223,describing a steerable bird that is designed to be electrically andmechanically connected in series with a streamer; another suitabledevice is that known under the trade designation DigiBIRD™, availablefrom Input/Output, Inc., Stafford, Tex. Other streamer positioningdevices, such as the devices described in U.S. Pat. Nos. 3,774,570;3,560,912; 5,443,027; 3,605,674; 4,404,664; 6,525,992 and EP patentpublication no. EP 0613025, may be employed.

Systems of the invention may communicate with the outside world, forexample another vessel or vehicle, a satellite, a hand-held device, aland-based device, and the like. The way this may be accomplished variesin accordance with the amount of energy the system requires and theamount of energy the system is able to store locally in terms ofbatteries, fuel cells, and the like. Batteries, fuel cells, and the likemay be employed, and wireless communication may be sufficient.Alternatively, or in addition, there may be a hard-wire power connectionand a hard wire communications connection to another device, this otherdevice able to communicate via wireless transmission.

Certain systems and methods of the invention may work in feed-forwardedfashion with existing control apparatus and methods to position not onlythe tow vessels, but seismic sources and streamers. Sources andstreamers may be actively controlled by using GPS data or other positiondetector sensing the position of the streamer (e.g. underwater acousticnetwork), or other means may sense the orientation of one or moreindividual streamers (e.g. compass) and feed this data to navigation andcontrol systems. While gross positioning and local movement of one ormore tracking points, centers of sources and/or a streamer front endcenter may be controlled via controlling one or more tow vessels, finecontrol may be accomplished on some other vessel, locally, or indeed aremote location. By using a communication system, either hardwire orwireless, environmental information ahead of the vessel may be sent toone or more local controllers, as well as the controller for eachvessel. The local controllers may in turn be operatively connected tospread control elements comprising motors or other motive power means,and actuators and couplers connected to the orientation members (flaps),and, if present, steerable birds, which function to move the spreadcomponents as desired. This in turn adjusts the position of the spreadelement, causing it to move as desired. Feedback control may be achievedusing local sensors positioned as appropriate depending on the specificembodiment used, which may inform the local and remote controllers ofthe position of one or more orientation members, distance betweenstreamers, a position of an actuator, the status of a motor or hydrauliccylinder, the status of a steerable bird, and the like. A computer orhuman operator can thus access information and control the entirepositioning effort, and thus obtain much better control over the seismicdata acquisition process.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims. In the claims, no clauses are intended to be inthe means-plus-function format allowed by 35 U.S.C. § 112, paragraph 6unless “means for” is explicitly recited together with an associatedfunction. “Means for” clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures.

1. A method comprising: (a) deploying a marine seismic spread comprisinga plurality of source-only tow vessels each towing one or more marineseismic sources without streamers, and one or more source-streamer towvessels, each towing one or more marine seismic sources and one or moreseismic streamers; and (b) positioning the plurality of source-only towvessels and the one or more source-streamer tow vessels to acquire awide- and/or full-azimuth seismic survey without need for the spread torepeat a path once traversed.
 2. The method of claim 1 wherein thedeploying of one or more source-streamer tow vessels comprises deployinga single source-streamer tow vessel.
 3. The method of claim 2 comprisingpositioning one or more source-only tow vessels starboard of thestreamers and one or more source-only tow vessels port of the streamers,wherein the starboard and port distances are either the same ordifferent.
 4. The method of claim 2 comprising deploying one or morestarboard source-only tow vessels ahead of and starboard of thestreamers, and one or more source-only tow vessel behind of andstarboard of the streamers, while deploying a similar arrangement on theport side, thereby acquiring two source lines simultaneously withsplit-spread configuration.
 5. The method of claim 1 comprisingdeploying two or more streamer-source tow vessels each towing aplurality of streamers.
 6. The method of claim 1 comprising acquiringtwo source lines of marine seismic data simultaneously with split-spreadconfiguration, comprising deploying a single source-streamer tow vesseltowing a plurality of streamers, and deploying all of the source-onlytow vessels on the starboard or all on the port side of the singlesource-streamer tow vessel to acquire a wide- and/or full azimuthseismic survey.
 7. The method of claim 6 comprising deploying two ormore source-only tow vessels port of or starboard of and positionedahead of the streamers, and deploying two more source-only tow vesselsport of or starboard of and positioned behind the streamers.
 8. Themethod of claim 6 comprising deploying two or more sources utilizing thesame source-only tow vessels.
 9. The method of claim 1 comprisingcontrolling the one or more source-only tow vessels and/or the one ormore source-streamer tow vessels with one or more controllers alone orin conjunction with other controllers.
 10. The method of claim 9 whereinthe one or more controllers comprises one or more controllers selectedfrom PI, PD, PID, feed forward, cascade, internal feedback, modelpredictive, neural networks, Kalman filtering, and combinations thereof.11. The method of claim 9 wherein the one or more controllers comprisestwo or more controllers, each controller adapted to compute a residualequal to a difference in a tracking point 3D coordinate position andpre-plot track and a set point based on each residual, and wherein thetracking points are selected from a center of a source, a streamer frontend center, and an imaginary tracking point between a source and thestreamers.
 12. The method of claim 1 wherein the source-streamer towvessel does not tow a source, or the source is inactive.
 13. A methodcomprising: (a) deploying a marine seismic spread comprising asource-streamer tow vessel towing one or more marine seismic sources andone or more seismic streamers, a port source-only tow vessel, and astarboard source-only tow vessel; and (b) positioning the source-onlytow vessels and the source-streamer tow vessel to acquire a wide- and/orfull-azimuth seismic survey without need for the spread to repeat a pathonce traversed, and acquiring two source lines of marine seismic datasimultaneously with split-spread configuration.
 14. A system comprising:(a) a marine seismic spread comprising a plurality of source-only towvessels each adapted to tow one or more marine seismic sources withoutstreamers, and one or more source-streamer tow vessels each adapted totow one or more marine seismic sources and one or more seismicstreamers; (b) the source-only tow vessels and the source-streamer towvessels adapted to be positioned to acquire a wide- and/or full azimuthseismic survey without need for the source-streamer vessels to repeat apath once traversed.
 15. The system of claim 14 configured to acquiretwo source lines of marine seismic data simultaneously with split-spreadconfiguration.
 16. The system of claim 14 comprising one or morereceiver positioning apparatus or systems, one or more sourcepositioning apparatus or systems, one or more streamer steering devices,one or more source array steering devices, one or more noise attenuationapparatus or systems, and combinations thereof.
 17. The system of claim14 configured to utilize sequential source shooting or, alternatively,two or more sources may be shot simultaneously, with the sources beingencoded so that they may be distinguished during data interpretation.18. The system of claim 14 configured to acquire two source lines ofmarine seismic data simultaneously with split-spread configurationwherein the plurality of source-only tow vessels comprises twosource-only tow vessels following substantially the same path or line,either port or starboard of a streamer-only tow vessel travelingsubstantially parallel to the path of the source-only tow vessels. 19.The system of claim 14 comprising one or more controllers adapted tocontrol position of one or more tracking points, the tracking pointsselected from a center of a source, a streamer front end center, astreamer back end center, a tracking point somewhere between a center ofsource and a streamer front end center, a center of a plurality ofstreamers, and a front of any one streamer.
 20. The system of claim 14wherein the one or more source-streamer tow vessels is a single vessel,and a source associated with the source-streamer tow vessel isinactivated or removed. 21-40. (canceled)